This section is intended to introduce various aspects of the art, which may be associated with exemplary embodiments of the present disclosure. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present disclosure. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of prior art.
Recycling is the process of collecting and processing materials that would otherwise be thrown away as trash, and turning them into new products. Recycling has benefits for communities and for the environment, since it reduces the amount of waste sent to landfills and incinerators, conserves natural resources such as timber, water, and minerals, increases economic security by tapping a domestic source of materials, prevents pollution by reducing the need to collect new raw materials, and saves energy. After collection, recyclables are generally sent to a material recovery facility to be sorted, cleaned, and processed into materials that can be used in manufacturing. As a result, high throughput automated sorting platforms that economically sort highly mixed waste streams would be beneficial throughout various industries. Thus, there is a need for cost-effective sorting platforms that can identify, analyze, and separate mixed industrial or municipal waste streams with high throughput to economically generate higher quality feedstocks (which may also include lower levels of trace contaminants) for subsequent processing. Typically, material recovery facilities are either unable to discriminate between many materials, which limits the scrap to lower quality and lower value markets, or too slow, labor intensive, and inefficient, which limits the amount of material that can be economically recycled or recovered.
Moreover, high throughput technologies for improving liberation of complex scrap/joint streams are needed for all material classes. For example, consumer products often contain both metals and plastics, but with today's technologies, they cannot be effectively and economically recycled for several reasons, including that there are no existing technologies that can rapidly sort these materials for subsequent recovery and processing. Additionally, recycled paper streams (fibers) are often contaminated with ink, adhesives, glass, wood, plastic, shards, flexible films, and organics causing down-grading of waste paper and cardstock. Current sorting processes do not include contaminate removal steps, and contaminated secondary material flows limit the markets and value of the fiber products. Therefore, solutions are needed that can more effectively identify and remove glass, food, and contaminants from paper feedstocks.
In the case of recycling of electronic waste (“e-waste”), separations are generally physical for plastics and chemical for materials. To increase domestic recycling of such e-waste, high throughput approaches for separating e-waste for metals and plastics are needed which are both energy efficient and cost-effective. Additionally, existing sorting technologies have a very limited capability to separate plastics with similar densities. Such complex streams may include both joined and un-joined materials (e.g., plastics, e-waste, auto, etc.). Therefore, more energy-efficient processing methodologies that enable high-resolution sorting of specific complex mixed material streams are needed.
And, there are very few, if any, cost and energy effective recycling technologies for low value waste plastics. As a result, such low value plastics (e.g., carpets and carpet residues, tires, tennis shoes, etc.) have no effective material recovery path. Therefore, technologies for cost-effective and more energy efficient sorting of such low value plastics are needed to generate high value and high purity feedstocks from polymers (carpets, residues, etc.) and natural fibers (cotton/other cellulosic materials).
Scrap metals are often shredded, and thus require sorting to facilitate reuse of the metals. By sorting the scrap metals, metal is reused that may otherwise go to a landfill. Additionally, use of sorted scrap metal leads to reduced pollution and emissions in comparison to refining virgin feedstock from ore. Scrap metals may be used in place of virgin feedstock by manufacturers if the quality of the sorted metal meets certain standards. The scrap metals may include types of ferrous and nonferrous metals, heavy metals, high value metals such as nickel or titanium, cast or wrought metals, and other various alloys.
Wrought scrap can contain a mixture of wrought alloys. The mixed wrought scrap has limited value because the mixture, due to its combined chemical composition, must be diluted if used to produce a new wrought alloy. The reason this is so is due to the more stringent compositional tolerances of wrought alloys, which are required to meet the performance requirements of wrought products. High quality scrap should have a high absorption back into the recycled product. High absorption means that a substantial portion of the final product is composed of scrap. To increase the value of the wrought scrap requires the separation of wrought product into alloy grades or similar constituted materials to maximize absorption. Absorption is defined as the percentage of an alloy or mixture that can be used to produce an ingot of another desired composition without exceeding the specified alloy composition limits. Mixed alloy scrap presents some difficult problems in separability due to its poor absorption into high quality wrought alloys. Mixed alloy scrap has poor absorption into high quality wrought alloys, and as a result, only limited amounts of mixed scrap can be used for recycling into wrought products.
The recycling of aluminum scrap is a very attractive proposition in that up to 95% of the energy costs associated with manufacturing can be saved when compared with the laborious extraction of the more costly primary aluminum. Primary aluminum is defined as aluminum originating from aluminum-enriched ore, such as bauxite. At the same time, the demand for aluminum is steadily increasing in markets, such as car manufacturing, because of its lightweight properties. Correspondingly, it is particularly desirable to efficiently separate aluminum scrap metals into alloy families, since mixed aluminum scrap of the same alloy family is worth much more than that of indiscriminately mixed alloys. For example, in the blending methods used to recycle aluminum, any quantity of scrap composed of similar, or the same, alloys and of consistent quality, has more value than scrap consisting of mixed aluminum alloys. Within such aluminum alloys, aluminum will always be the bulk of the material. However, constituents such as copper, magnesium, silicon, iron, chromium, zinc, manganese, and other alloy elements provide a range of properties to alloyed aluminum and provide a means to distinguish one wrought alloy from the other.
The Aluminum Association is the authority that defines the allowable limits for aluminum alloy chemical composition. The data for the alloy chemical compositions is published by the Aluminum Association in “International Alloy Designations and Chemical Composition Limits for Wrought Aluminum and Wrought Aluminum Alloys,” which was updated in January 2015, and which is incorporated by reference herein. The Aluminum Association also has a similar document for cast alloys. In general, according to the Aluminum Association, the 1000 series of aluminum alloys is composed essentially of pure aluminum with a minimum 99% aluminum content by weight; the 2000 series is aluminum principally alloyed with copper; the 3000 series is aluminum principally alloyed with manganese; the 4000 series is aluminum alloyed with silicon; the 5000 series is aluminum primarily alloyed with magnesium; the 6000 series is aluminum alloyed with magnesium and silicon; the 7000 series is aluminum primarily alloyed with zinc; and the 8000 series is a miscellaneous category.
While it would therefore be beneficial to be able to sort a mass or body of aluminum scrap containing a heterogeneous mixture of pieces of different alloys, to separate the different alloy compositions or at least different alloy families before re-melting for recycling, scrap pieces of different aluminum alloy compositions are not ordinarily visually distinguishable from each other. Optically indistinguishable metals (especially alloys of the same metal) are difficult to sort. For example, it is not easy to manually separate and identify small pieces of cast from wrought aluminum or to spot zinc or steel attachments encapsulated in aluminum. There also is the problem that color sorting is nearly impossible for identically colored materials, such as the all-gray metals of aluminum alloys, zinc, and lead.
Furthermore, the presence of commingled pieces of different alloys in a body of scrap limits the ability of the scrap to be usefully recycled, unless the different alloys (or, at least, alloys belonging to different compositional families such as those designated by the Aluminum Association series 1000, 2000, 3000, etc.) can be separated prior to re-melting. This is because, when commingled scrap of plural different alloy compositions or composition families is re-melted, the resultant molten mixture contains proportions of the principle alloy and elements (or the different compositions) that are too high to satisfy the compositional limitations required in any particular commercial alloy.
Moreover, as evidenced by the production and sale of the Ford F-150 pickup having a considerable increase in its body and frame parts consisting of aluminum instead of steel, it is additionally desirable to recycle sheet metal scrap, including that generated in the manufacture of automotive components from sheet aluminum. Recycling of the scrap involves re-melting the scrap to provide a body of molten metal that can be cast and/or rolled into useful aluminum parts for further production of such vehicles. However, automotive manufacturing scrap (and metal scrap from other sources such as airplanes and commercial and household appliances) often includes a mixture of scrap pieces of wrought and cast pieces and/or two or more aluminum alloys differing substantially from each other in composition. A specific example of mixed manufacturing scrap of aluminum sheet, generated in certain present-day automotive manufacturing operations, is a mixture of pieces of one or more alloys of the Aluminum Association 5000 series and pieces of one or more alloys of the Aluminum Association 6000 series. Thus, those skilled in the aluminum alloy art will appreciate the difficulties of separating aluminum alloys, especially alloys that have been worked, such as cast, forged, extruded, rolled, and generally wrought alloys, into a reusable or recyclable worked product. These alloys for the most part are indistinguishable upon visual inspection or by other conventional scrap sorting techniques, such as density and/or eddy-current techniques. Therefore, it is a difficult task to separate, for example, 2000, 3000, 5000, 6000, and 7000 series alloys; moreover, the ability to sort between aluminum alloys within the same Aluminum Association series has not been accomplished in the prior art.
As a result, there are certain economies available to the aluminum industry by developing a well-planned yet simple recycling plan or system. The use of recycled material would be a less expensive metal resource than a primary source of aluminum. As the amount of aluminum sold to the automotive industry (and other industries) increases, it will become increasingly necessary to use recycled aluminum to supplement the availability of primary aluminum.